Avoid unwanted project persistence. (#1009)

Session storage lasts for the lifetime of the tab, so we need to make
sure subsequent migration URLs and iframe configurations work.

Motivated by issues with "Open in Classroom" and "Open in Python" on microbit.org.

Author: microbit-matt-hillsdon

package-lock.json

@@ -10,20 +10,15 @@ import {
 import { fromByteArray, toByteArray } from "base64-js";
 import EventEmitter from "events";
 import sortBy from "lodash.sortby";
+import { lineNumFromUint8Array } from "../common/text-util";
 import { BoardId } from "../device/board-id";
 import { FlashDataSource, HexGenerationError } from "../device/device";
 import { Logging } from "../logging/logging";
-import { Host } from "./host";
+import { MicroPythonSource } from "../micropython/micropython";
 import { asciiToBytes, generateId } from "./fs-util";
-import {
-  FSStorage,
-  InMemoryFSStorage,
-  SessionStorageFSStorage,
-  SplitStrategyStorage,
-} from "./storage";
+import { Host } from "./host";
 import { PythonProject } from "./initial-project";
-import { lineNumFromUint8Array } from "../common/text-util";
-import { MicroPythonSource } from "../micropython/micropython";
+import { FSStorage } from "./storage";
 
 const commonFsSize = 20 * 1024;
 
@@ -168,11 +163,7 @@ export class FileSystem extends EventEmitter implements FlashDataSource {
     private microPythonSource: MicroPythonSource
   ) {
     super();
-    this.storage = new SplitStrategyStorage(
-      new InMemoryFSStorage(undefined),
-      SessionStorageFSStorage.create(),
-      logging
-    );
+    this.storage = host.createStorage(logging);
     this.project = {
       files: [],
       id: generateId(),
@@ -216,7 +207,7 @@ export class FileSystem extends EventEmitter implements FlashDataSource {
     if (!this.initializing) {
       this.initializing = (async () => {
         this._dirty = await this.storage.isDirty();
-        if (!(await this.exists(MAIN_FILE))) {
+        if (await this.host.shouldReinitializeProject(this.storage)) {
           // Do this ASAP to unblock the editor.
           this.cachedInitialProject = await this.host.createInitialProject();
           if (this.cachedInitialProject.projectName) {

src/fs/fs.ts

@@ -18,6 +18,12 @@ import {
   projectFilesToBase64,
 } from "./initial-project";
 import { parseMigrationFromUrl } from "./migration";
+import {
+  FSStorage,
+  InMemoryFSStorage,
+  SessionStorageFSStorage,
+  SplitStrategyStorage,
+} from "./storage";
 
 const messages = {
   type: "pyeditor",
@@ -30,22 +36,45 @@ const messages = {
 };
 
 export interface Host {
+  createStorage(logging: Logging): FSStorage;
+  shouldReinitializeProject(storage: FSStorage): Promise<boolean>;
   createInitialProject(): Promise<PythonProject>;
   notifyReady(fs: FileSystem): void;
 }
 
 export class DefaultHost implements Host {
   constructor(private url: string = "") {}
 
-  async createInitialProject(): Promise<PythonProject> {
+  createStorage(logging: Logging): FSStorage {
+    return new SplitStrategyStorage(
+      new InMemoryFSStorage(undefined),
+      SessionStorageFSStorage.create(),
+      logging
+    );
+  }
+
+  async shouldReinitializeProject(storage: FSStorage): Promise<boolean> {
     const migration = parseMigrationFromUrl(this.url);
     if (migration) {
-      return {
+      return true;
+    }
+    return !(await storage.exists(MAIN_FILE));
+  }
+
+  async createInitialProject(): Promise<PythonProject> {
+    const migrationParseResult = parseMigrationFromUrl(this.url);
+    if (migrationParseResult) {
+      const { migration, postMigrationUrl } = migrationParseResult;
+      const project = {
         files: projectFilesToBase64({
           [MAIN_FILE]: migration.source,
         }),
         projectName: migration.meta.name,
       };
+      // Remove the migration information from the URL so that a refresh
+      // will reload from storage not remigrate.
+      window.history.replaceState(null, "", postMigrationUrl);
+      return project;
     }
     return defaultInitialProject;
   }
@@ -58,6 +87,13 @@ export class IframeHost implements Host {
     private window: Window,
     private debounceDelay: number = 1_000
   ) {}
+  createStorage(logging: Logging): FSStorage {
+    return new InMemoryFSStorage(undefined);
+  }
+  async shouldReinitializeProject(storage: FSStorage): Promise<boolean> {
+    // If there is persistence then it is the embedder's problem.
+    return true;
+  }
   createInitialProject(): Promise<PythonProject> {
     return new Promise((resolve) => {
       this.window.addEventListener("load", () =>

src/fs/host.ts

@@ -7,19 +7,23 @@ import { isMigration, parseMigrationFromUrl } from "./migration";
 
 // The heart project.
 export const testMigrationUrl =
-  "http://localhost:3000/#import:#project:XQAAgACRAAAAAAAAAAA9iImmlGSt1R++5LD+ZJ36cRz46B+lhYtNRoWF0nijpaVyZlK7ACfSpeoQpgfk21st4ty06R4PEOM4sSAXBT95G3en+tghrYmE+YJp6EiYgzA9ThKkyShWq2UdvmCzqxoNfYc1wlmTqlNv/Piaz3WoSe3flvr/ItyLl0aolQlEpv4LA8A=";
+  // origin needs to match jest's testUrl
+  "http://localhost/#import:#project:XQAAgACRAAAAAAAAAAA9iImmlGSt1R++5LD+ZJ36cRz46B+lhYtNRoWF0nijpaVyZlK7ACfSpeoQpgfk21st4ty06R4PEOM4sSAXBT95G3en+tghrYmE+YJp6EiYgzA9ThKkyShWq2UdvmCzqxoNfYc1wlmTqlNv/Piaz3WoSe3flvr/ItyLl0aolQlEpv4LA8A=";
 
 describe("parseMigrationFromUrl", () => {
   it("parses valid URL", () => {
     const migration = parseMigrationFromUrl(testMigrationUrl);
     expect(migration).toEqual({
-      meta: {
-        cloudId: "microbit.org",
-        comment: "",
-        editor: "python",
-        name: "Hearts",
+      migration: {
+        meta: {
+          cloudId: "microbit.org",
+          comment: "",
+          editor: "python",
+          name: "Hearts",
+        },
+        source: `from microbit import *\r\ndisplay.show(Image.HEART)`,
       },
-      source: `from microbit import *\r\ndisplay.show(Image.HEART)`,
+      postMigrationUrl: "http://localhost/",
     });
   });
   it("undefined for nonsense", () => {

src/fs/migration.test.ts

@@ -23,14 +23,25 @@ export const isMigration = (v: any): v is Migration =>
   typeof v.meta?.name === "string" &&
   typeof v.source === "string";
 
-export const parseMigrationFromUrl = (url: string): Migration | undefined => {
-  const urlPart = url.split("#project:")[1];
+interface MigrationParseResult {
+  migration: Migration;
+  postMigrationUrl: string;
+}
+
+export const parseMigrationFromUrl = (
+  url: string
+): MigrationParseResult | undefined => {
+  const parts = url.split("#project:");
+  const urlPart = parts[1];
   try {
     if (urlPart) {
       const bytes = toByteArray(urlPart);
       const json = JSON.parse(LZMA.decompress(bytes));
       if (isMigration(json)) {
-        return json;
+        let postMigrationUrl = parts[0];
+        // This was previously stripped off by the versioner but for now do it ourselves:
+        postMigrationUrl = postMigrationUrl.replace(/#import:$/, "");
+        return { migration: json, postMigrationUrl };
       }
     }
   } catch (e) {